A substantial number of graphic recording systems have been developed to provide automated or computer controlled graphic recording upon a media. While the individual structures of such graphic recorders vary substantially, generally all include a media transport system in which the media is moved in a first direction and a moveable pen carriage supported and controlled to provide motion of the pen carriage in a second direction relative to media motion. In most instances, the directions of media movement and pen carriage movement are orthogonal.
With the development of computer drive systems having increased capability, there arose a need to provide graphic recording systems employing a plurality of recording pens which commonly facilitated multiple color selection.
One example of a multiple pen graphic recorder is set forth in U.S. Pat. No. 3,401,401 issued Sept. 10, 1968 to Read et al. for Multiple Pen Carriage. The device set forth in Read provides four pens supported on a moveable carriage together with a corresponding group of four independent actuating devices each operative upon one of the pens. The use of multiple actuating devices supported on the moveable carriage substantially increases the overall mass of the pen carriage which in turn substantially limits the speed and acceleration of pen carriage motion.
Another example of prior art multiple pen graphic recorders is set forth in U.S. Pat. No. 4,135,245 issued Jan. 16, 1979 to Kemplin et al. for Plotter With Automatic Pen Changer. The system set forth in Kemplin utilizes a stationary pen repository in which multiple pens are maintained. A moveable recording head is configured to receive and support a single recording pen and means are provided for interrupting the recording process in order to exchange the pen supported by the recording head with a different pen in the stationary pen repository. While the system set forth in Kemplin avoids the increase of pen carriage mass caused in the Read System, it increases the recording time due to the interruption of recording during pen substitution.
Still another example of multiple pen graphic recording systems is set forth in U.S. patent application Ser. No. 4,500,890 issued Feb. 19, 1985 to Nicholas for Graphic Recording System which is commonly owned with the present invention. The system set forth in Nicholas provides a moveable carriage supporting a plurality of recording pens together with a single actuator selectively operative upon the pens.
Still another example of multiple pen graphic recording systems is set forth in U.S. Pat. No. 4,578,683 issued Mar. 25, 1986 to Gordon and entitled Graphic Recording System which is commonly owned with the present invention. In the Gordon System, a moveable pen carriage supports a plurality of recording elements. The carriage is moveable in two directions along a path relative to the recording media and an associated actuator arm mechanism is moveably supported on a rod. The rod has its longitudinal axis generally parallel to the carriage path. Stationary operating means are coupled to the rod and are operative to move the selected pen into engagement with the recording media. The system set forth in Gordon provides substantial advantage over the prior art systems in its avoidance of powered actuating means upon the pen carriage and its reduction of overall mass of the pen carriage.
While the foregoing described prior art graphic recording systems facilitate multiple pen carriage recording and exhibit several advantages, there remains a need in the art for a graphic recording system having a lightweight moveable pen carriage and pen selecting means which simultaneously reduces overall pen carriage mass, avoids the need of supporting powered pen selection mechanisms upon the moveable carriage and provides accurate controllable pen selection and motion.